This invention is generally directed to magnetic nanocomposite compositions and processes for the preparation thereof, and more specifically the present invention is directed to a magnetic nanocomposite composition of nanocrystalline Fe.sub.3 O.sub.4, or ferric oxide particles that are formed in and stabilized by an ion binding polymeric matrix. The nanocomposite compositions of the present invention in one embodiment contain nanocrystalline Fe.sub.3 O.sub.4 particles, and an ion exchange resin as a polymeric matrix host for the nanocrystalline Fe.sub.3 O.sub.4 particles. The nanocomposite compositions of the present invention in one embodiment can be prepared by processes comprising loading an ionic exchange resin with aqueous Fe(II) ions, and subsequently treating the resin bound Fe(II) ions successively with an aqueous base and aqueous salt such as an alkali metal sulfide, especially sodium sulfide, in the presence of oxygen. The resulting highly black colored and magnetic nanocomposite Fe.sub.3 O.sub.4 -polymer compositions and of the present invention are useful in magnetic applications, for example, magnetic imaging and printing with dry and liquid developer compositions, and for electrophotography. These materials possess electronic, optical, magnetic and chemical properties due primarily to the extremely small dimensions, for example, about 1.0 to about 100 nanometers of the nanocrystalline Fe.sub.3 O.sub.4 particles in the nanocomposite.
An important problem which has limited the preparation and maintenance of nanoscale materials is the tendency of the initially small atomically clustered particles to aggregate into larger masses to reduce the energy associated with the high surface area to volume ratio of the nanosized particles. In the aforementioned U.S. Pat. No. 4,474,866, a polymeric matrix, for example, a synthetic ion exchange resin is used to prepare, stabilize, isolate, and characterize related nanocrystalline Fe.sub.2 O.sub.3 particles as a magnetic polymer composite. In the present invention, there were formulated nanocrystalline composites comprised of Fe.sub.3 O.sub.4 rather than Fe.sub.2 O.sub.3 since Fe.sub.3 O.sub.4 possesses, for bulk materials, about a 20 to about 26 percent greater specific magnetization. The Fe.sub.3 O.sub.4 resin nanocomposites of the present invention may be post processed and milled to form magnetic composite particles which are useful in formulating aqueous dispersible magnetic fluids and preparing magnetic polymer films.
Prior art formation of submicron or nanometer structures have predominantly included the formation of large particles which are subsequently ground or milled until particles of the desired size are achieved. The grinding and milling times associated with the formation of such particles ranged from 120 to about 2,900 hours. A method of forming dry magnetic submicron particles by precipitation of a magnetic oxide in an ion exchange resin is exemplified by Ziolo in the aforementioned U.S. Pat. No. 4,474,866. According to the method employed therein, an ion exchange resin is loaded with a magnetic ion and chemically converted to a magnetic oxide Fe.sub.2 O.sub.3. The magnetic loaded ion exchange resin is then recovered and dried. The magnetic polymer resin is then optionally micronized to form a fine magnetic powder.
U.S. Pat. No. 4,101,435 to Hasegawa et al., issued Jul. 18, 1978, discloses a magnetic iron oxide-dextran complex. This compound can be produced by reacting an aqueous sol of magnetic iron oxide with dextran having an intrinsic viscosity of about 0.02 to about 0.5 at an elevated temperature in an aqueous medium, and is useful not only in pharmaceutical and medical fields as a hematinic medium, a radiopaque medium, a blood measuring agent, or a carrier for a medicinal substance, but also in wide range of other technological fields where its magnetic property can be utilized.
U.S. Pat. No. 4,873,102 to Chang et al., issued Oct. 10, 1989, discloses magnetic polymer particles that are formed by swelling porous, polymer particles and impregnating the particles with an aqueous solution of a precursor magnetic metal salt such as an equimolar mixture of ferrous chloride and ferric chloride. On addition of a basic reagent such as dilute sodium hydroxide, the metal salts are converted to crystals of magnetite which are uniformly contained throughout the pores of the polymer particle. The magnetite content can be increased and neutral buoyancy achieved by repetition of impregnation and neutralization steps to adjust the magnetite content to a desired level.
U.S. Pat. No. 4,977,053 to Ohishi et al., issued Dec. 11, 1990, discloses a toner comprising colored particles and a magnetic shell coated thereon, wherein the colored particles are comprised of a binder resin and a coloring agent, and the magnetic shell is formed from an iron oxide type magnetic material. The toner can be fixable at a low temperature or a low pressure, but the toner particles do not agglomerate with each other during long-term storage.
U.S. Pat. No. 5,039,559 to Sang et al., issued Aug. 13, 1991, discloses magnetically attractable particles comprised of a core of magnetic material encapsulated in a metal oxide coating. These particles can be prepared by emulsifying an aqueous solution or dispersion of the magnetic material or precursor, and an aqueous solution or sol of a coating inorganic oxide or precursor, in an inert water-immiscible liquid. The aqueous droplets are gelled, e.g. by ammonia or an amine, recovered, and heated at 250.degree.-2,000.degree. C. The resulting particles are generally smooth spheres below 100 microns in diameter and often of sub-micron size.
U.S. Pat. No. 5,137,796 to Takiguchi et al., issued Aug. 11, 1992, discloses a magnetic developer for developing an electrostatic latent image, including hydrophobic silica fine powder and an insulating magnetic toner comprising at least a binder resin and a magnetic material comprising spherical magnetic particles; wherein 0.16 to 1.6 wt. parts of the hydrophobic silica fine powder is mixed with 100 wt. parts of the insulating magnetic toner. The developer contains 17-60% by number of magnetic toner particles having a particles size of 5 microns of smaller, 5-50% by number of magnetic toner particles having a particle size of 6.35-10.08 microns, and 2.0% by volume or less of magnetic toner particles having a particle size of 12.7 microns or larger.
U.S. Pat. No. 5,204,457 to Maruno et al., issued Apr. 20, 1993, discloses a complex of a carboxyalkyl ether of polysaccharide with a magnetic metal oxide. This complex is extremely excellent in stability in preservation in the form of aqueous sol and has only a low toxicity, and thus is useful, for example, for medical use as a nuclear magnetic imaging molding agent or the like.
Two examples of the many patents which disclose magnetite containing or magnetic toners are U.S. Pat. No. 5,045,423, and U.S. Pat. No. 4,973,538, the disclosure of which are totally incorporated herein by reference.
There remains a need for an economic and convenient process of obtaining very small magnetic particles and magnetic polymeric materials, and more specifically micron and submicron magnetic polymeric particles, without the complications and disadvantages of the aforementioned prior art. Further, there is a need for convenient means for a preparing nanocrystalline iron sulfur and Fe.sub.3 O.sub.4 containing polymeric composites without the need of having to resort to intensive and expensive particle size reduction or comminution processes for obtaining clean, optionally dry and small composite particles of magnetic nanocrystalline particles contained in a polymeric matrix, for example, from less than about 0.1 to about 100 microns in volume average diameter as determined by a scanning electron microscope or Malvern System 3601 particle size analyzer. Still further, there is a need for nanocomposite nanocrystalline particles that permit low cost, clean, and optionally dry micron and submicron polymeric composite particles that can be selected as a magnetic liquid, and utilized as a component in dry electrophotographic developer compositions, carrier powder coatings, photoconductor pigment or resin coating suspensions, and as toner additives for enhanced photoreceptor development and cleaning.